This is the fourth biannual Gordon Research Conference on Mutagenic Mechanisms, now alternating with conferences on genetic toxicology. The conference aims to address in a single meeting the diverse research areas crucial to determining how mutations arise. The meetings are attended by over 100 scientists from many countries, representing universities, research institutes, industries and governmental agencies. The conference will consist of nine sessions, each including about three scheduled speakers, plus extensive audience discussion. Poster sessions will provide an opportunity for all to present recent work in further detail. Discussion leaders and speakers are being drawn from outstanding and innovative scientists such as Maurice Fox (MIT), Barry Glickman (NIEHS), Frank Hutchinson (Yale), Tomas Lindah1, ICRF, London), Teiichi Minagawa (Kyoto, Japan), Lynn Ripley (NIEHS) and Graham Walker (MIT). The sessions will cover mis-match repair, the enzymatic basis of damage-bypass mutagenesis, the repair of alkylation damage, analysis of mutational spectra by different agents, the mechanism of polymerase fidelity and the role of associated proteins, the T4 WXY system, the role of alternative DNA structure in mutagenesis and the recent developments on error-prone repair. The impact of such an international and multidisciplinary conference should lead to major new contributions towards understanding processes that contribute to toxicological endpoints, such as birth defects, carcinogenesis, and possibly heart diseases and aging.